This application claims the priority of German Patent Application, Serial No. 299 07 531.1, filed Apr. 28, 1999, the subject matter of which is incorporated herein by reference.
The present invention relates, in general, to a device providing positioning, registration and displacement, in particular for projection devices, and is useful in device manufacturing, such as projection mask aligners, and for measurement that requires high-precision alignment, such as scanning electron microscopy.
A precision positioning device requires a stable actuating and operating mechanisms, in particular for the output stage of the drives, to achieve the required accuracy. These requirements can be satisfied by displacement devices which have flexible elements but do not have kinematic mechanisms in the last stage, making it possible to tension the elements that transfer the motion to the maximum limit.
A device employing cylinders or rollers to provide a displacement is known from Author""s Certificate, No. 1430990, issued Oct. 29, 1984. The device includes three flexible connections, with one connection stacked on top of the next, wherein the ends of the upper flexible connection area are secured to the movable element and the ends of the lower flexible connection are secured to the housing. This device incorporates rollers and suffers shortcomings as a consequence of a third flexible connection which results in a relative complex configuration. Moreover, the device has a limited range because the flexible connections are fixedly attached to the roller.
Another displacement device is disclosed in Author""s Certificate, No. 1439686, issued Jul. 30, 1986. This device includes a moveable housing, a movable element and two flexible elements of different thickness, wherein the ends of the elements are fixedly attached to respective elements on the circumference of the drum and the support rollers with a loop. This device is also relatively complex due to the additional support rollers. In addition, the friction forces are higher as a consequence of internal expansion forces between the drum, the rollers and the housing, which when taken together decrease the positional accuracy of the movable element.
It is thus an object of the present invention to provide an improved displacement device, obviating the afore-stated drawbacks.
In particular, it is an object of the present invention to provide an improved displacement device which is simple in design and increases the positional accuracy during displacement.
These objects, and others which will become apparent hereinafter, are attained in accordance with the present invention by providing a housing, an element which is movable relative to the housing, and a moveable drum which is enveloped by flexible elements, with first ends of the flexible elements fixedly attached to the housing and the other ends of the flexible elements pretensioned and attached to the movable element on the diametrically opposed side of the drum.
Suitably, the drum has a stepped configuration, wherein the steps of the drum may advantageously aligned in an axial direction of the drum. The flexible elements may be placed on the different axial steps abound the drum, and/or the first ends of the flexible elements may be attached to the movable element by means of a traverse bar.
According to another feature of the present invention, the movable element may be designed as a single coordinate table movable in one direction relative to the housing. The flexible elements can further be implemented in the form of bands, made preferably of a metal.